Backport of unshare() syscall.
From uClibc git 19dd090a0f68765db87990ef8eda9bf77bb29581

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

---
diff -Nura uClibc-0.9.32.orig/libc/sysdeps/linux/common/bits/sched.h uClibc-0.9.32/libc/sysdeps/linux/common/bits/sched.h
--- uClibc-0.9.32.orig/libc/sysdeps/linux/common/bits/sched.h	2011-12-02 23:54:30.571841170 -0300
+++ uClibc-0.9.32/libc/sysdeps/linux/common/bits/sched.h	2011-12-02 23:57:45.874205079 -0300
@@ -58,7 +58,13 @@
 				      force CLONE_PTRACE on this clone.  */
 # define CLONE_CHILD_SETTID 0x01000000 /* Store TID in userlevel buffer in
 					  the child.  */
-# define CLONE_STOPPED	0x02000000 /* Start in stopped state.  */
+# define CLONE_STOPPED 0x02000000 /* Start in stopped state.  */
+# define CLONE_NEWUTS  0x04000000      /* New utsname group.  */
+# define CLONE_NEWIPC  0x08000000      /* New ipcs.  */
+# define CLONE_NEWUSER 0x10000000      /* New user namespace.  */
+# define CLONE_NEWPID  0x20000000      /* New pid namespace.  */
+# define CLONE_NEWNET  0x40000000      /* New network namespace.  */
+# define CLONE_IO      0x80000000      /* Clone I/O context.  */
 #endif
 
 /* The official definition.  */
@@ -74,11 +80,9 @@
 extern int clone (int (*__fn) (void *__arg), void *__child_stack,
 		  int __flags, void *__arg, ...) __THROW;
 
-#if 0
 /* Unshare the specified resources.  */
 extern int unshare (int __flags) __THROW;
 #endif
-#endif
 
 __END_DECLS
 
diff -Nura uClibc-0.9.32.orig/libc/sysdeps/linux/common/Makefile.in uClibc-0.9.32/libc/sysdeps/linux/common/Makefile.in
--- uClibc-0.9.32.orig/libc/sysdeps/linux/common/Makefile.in	2011-12-02 23:54:30.577841215 -0300
+++ uClibc-0.9.32/libc/sysdeps/linux/common/Makefile.in	2011-12-02 23:56:08.801527166 -0300
@@ -24,7 +24,8 @@
 	remap_file_pages.c sched_getaffinity.c sched_setaffinity.c \
 	sendfile64.c sendfile.c setfsgid.c setfsuid.c setresuid.c \
 	splice.c vmsplice.c tee.c signalfd.c swapoff.c swapon.c \
-	sync_file_range.c sysctl.c sysinfo.c timerfd.c uselib.c vhangup.c
+	sync_file_range.c sysctl.c sysinfo.c timerfd.c unshare.c uselib.c \
+	vhangup.c
 # NPTL needs these internally: madvise.c
 CSRC-$(findstring y,$(UCLIBC_LINUX_SPECIFIC)$(UCLIBC_HAS_THREADS_NATIVE)) += madvise.c
 ifeq ($(UCLIBC_HAS_THREADS_NATIVE),y)
diff -Nura uClibc-0.9.32.orig/libc/sysdeps/linux/common/stubs.c uClibc-0.9.32/libc/sysdeps/linux/common/stubs.c
--- uClibc-0.9.32.orig/libc/sysdeps/linux/common/stubs.c	2011-12-02 23:54:30.577841215 -0300
+++ uClibc-0.9.32/libc/sysdeps/linux/common/stubs.c	2011-12-02 23:58:18.803435042 -0300
@@ -278,6 +278,10 @@
 make_stub(umount2)
 #endif
 
+#if !defined __NR_unshare && defined __UCLIBC_LINUX_SPECIFIC__
+make_stub(unshare)
+#endif
+
 #ifndef __NR_utimensat
 make_stub(futimens)
 make_stub(utimensat)
diff -Nura uClibc-0.9.32.orig/libc/sysdeps/linux/common/unshare.c uClibc-0.9.32/libc/sysdeps/linux/common/unshare.c
--- uClibc-0.9.32.orig/libc/sysdeps/linux/common/unshare.c	1969-12-31 21:00:00.000000000 -0300
+++ uClibc-0.9.32/libc/sysdeps/linux/common/unshare.c	2011-12-02 23:58:42.693601880 -0300
@@ -0,0 +1,15 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * unshare() for uClibc
+ *
+ * Copyright (C) 2011 Henning Heinold <heinold@inf.fu-berlin.de>
+ *
+ * Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
+ */
+
+#include <sys/syscall.h>
+#include <sched.h>
+
+#if defined __NR_unshare
+_syscall1(int, unshare, int, flags)
+#endif